This invention relates generally to metal deforming operations, and, more particularly, to a process and apparatus for measuring unflatness of strip in a rolling mill.
Strip products of materials such as aluminum are typically manufactured by passing thick pieces of the material through a rolling mill. It is highly desirable that the rolled strip be flat over its entire length and width, and not have excessive residual stresses which would cause it to buckle, as such imperfections may cause the strip to break and may reduce fabricability in subsequent forming operations. Flatness and residual stress imperfections arise from a variety of causes, such as a rolling mill which is not level or has excessive dimensional variations along its axis, plugged coolant spray nozzles, tension asymmetries, and other causes which may be corrected by the mill operator or a process computer if the problem can be detected and recognized even as the rolling progresses. To this end, various types of on-line measuring equipment have been devised for monitoring a strip as it exits from the rolling mill.
Standard tensiometer rolls having a single pair of instrumented supports are commonly found in rolling mills. Such single-support tensiometer rolls can measure the total force and side-to-side differential force exerted by the strip on the roll, but not various other conditions of imperfect rolling, such as unflatness. For the latter condition, several methods of measurement have been proposed, including a series of commonly supported, laterally adjacent rollers which allow measurement of the strip tension at a series of points across the width of the roll. In another variation, coaxial rollers having a plurality of internal load cells similarly provide information concerning the distribution of strip tension across the width of the strip. From the distribution of strip tension, conclusions can be drawn about the flatness of the strip. In an alternative approach, photocells or other non-contact proximity sensors may be used to detect the flatness, thickness, or residual stress.
All of the previously proposed on-line flatness measurement processes and apparatus suffer from the common problem of extreme complexity and high maintenance cost. Some of the existing flatness measurement apparatus use a segmented roll body which may be the source of undesirable marking of the strip. Further, high capital investment costs are usually associated with such complex machines. Calibration of the multiple sensors or load cells typically involved in such apparatus is a continuing problem, particularly with apparatus employing photocells. In most instances, the complex apparatus is not usable in hot rolling operations because the measuring devices must be positioned too closely to the strip to be properly cooled.
Accordingly, there has been a continuing need for a less complex process and apparatus to detect mechanically induced rolling imperfections such as out-of-flatness conditions. Such apparatus should be highly reliable and easy to maintain, and be capable of detecting commonly occurring rolling problems. Preferably, such apparatus would be based upon a standard piece of apparatus already available in most strip rolling mills, so that capital investment costs and duplication of function would be minimized. The present invention fulfills this need, and further provides related advantages.